The present invention relates to an artificial airway device, and in particular to such a device which seeks to provide protection against gastric reflux.
For at least seventy years, endotracheal tubes comprising a long slender tube with an inflatable balloon disposed near the tube's distal end have been used for establishing airways in unconscious patients. In operation, the endotracheal tube's distal end is inserted through the mouth of the patient, into the patient's trachea. Once positioned, the balloon is inflated so as to form a seal with the interior lining of the trachea. After this seal is established, positive pressure may be applied to the tube's proximal end to ventilate the patient's lungs. Also, the seal between the balloon and the inner lining of the trachea protects the lungs from aspiration (e.g., the seal prevents material regurgitated from the stomach from being aspirated into the patient's lungs).
Although they have been successful, endotracheal tubes suffer from several major disadvantages. The principal disadvantage of the endotracheal tube relates to the difficulty of properly inserting the tube. Inserting an endotracheal tube into a patient is a procedure that requires a high degree of skill. Also, even for skilled practitioners, insertion of an endotracheal tube is sometimes difficult or not possible. In many instances, the difficulty of inserting endotracheal tubes has tragically led to the death of a patient because it was not possible to establish an airway in the patient with sufficient rapidity. Also, inserting an endotracheal tube normally requires manipulation of the patient's head and neck and further requires the patient's jaw to be forcibly opened widely. These necessary manipulations make it difficult, or undesirable, to insert an endotracheal tube into a patient who may be suffering from a neck injury.
The laryngeal mask airway device is a well known device that is useful for establishing airways in unconscious patients, and which seeks to address the above-described drawbacks associated with endotracheal tubes.
In contrast to the endotracheal tube, it is relatively easy to insert a laryngeal mask airway device into a patient and thereby establish an airway. Also, the laryngeal mask airway device is a “forgiving” device in that even if it is inserted improperly, it still tends to establish an airway. Accordingly, the laryngeal mask airway device is often thought of as a “life saving” device. Also, the laryngeal mask airway device may be inserted with only relatively minor manipulation of the patient's head, neck and jaw. Further, the laryngeal mask airway device provides ventilation of the patient's lungs without requiring contact with the sensitive inner lining of the trachea and the internal diameter of the airway tube is typically significantly larger than that of the endotracheal tube. Also, the laryngeal mask airway device does not interfere with coughing to the same extent as endotracheal tubes. Largely due to these advantages, the laryngeal mask airway device has enjoyed increasing popularity in recent years.
U.S. Pat. No. 4,509,514 describes a laryngeal mask airway device which consists of the basic parts which make up most if not all laryngeal mask airway devices, namely an airway tube opening at one end into the interior of a hollow mask portion shaped to fit readily behind the larynx of a patient. The periphery of the mask is formed by a cuff which in use forms a seal around the opening of the larynx. This enables the airway to be established effectively.
Laryngeal mask airway devices with specific provision for gastric-discharge drainage have been developed, as exemplified by U.S. Pat. No. 4,995,388 (FIGS. 7 to 10); U.S. Pat. No. 5,241,956; and U.S. Pat. No. 5,355,879. These devices generally incorporate a small-diameter drainage tube having an end located at the distal end of the mask, so as to lie against the upper end of the upper oesophageal sphincter when the mask is in place, the tube being of sufficient length to extend out of the mouth of the patient to enable active or passive removal of gastric discharge from the upper oesophageal sphincter. According to alternative proposals, the drainage tube may extend beyond the distal end of the mask, into the oesophagus itself (U.S. Pat. No. 4,995,388, FIGS. 7 and 11).
Such devices are generally useful in providing for extraction of regurgitated matter, but are still not always fully effective in preventing aspiration of gastric contents into the patient's lungs. In particular, where the gastric discharge is as a result of the patient vomiting, rather than merely from regurgitation of the gastric matter, the substantial pressure of the vomited matter may in certain cases be enough to dislodge the mask altogether, even where a drainage tube is provided, potentially affecting the integrity of the artificial airway and/or resulting in the vomited matter being aspirated into the lungs of the patient.
As will be appreciated, the potential for the mask to become dislodged under vomiting is also inherent in masks such as that disclosed by U.S. Pat. No. 4,509,514, which do not feature a drainage tube.
Particularly where a mask does not provide for gastric drainage, and even where a gastric drainage tube is provided, there is even a risk of a potentially fatal build up of pressure in the oesophagus if vomited matter cannot be effectively vented from the oesophagus, which might for example occur if the mask becomes jammed in the pharynx.
Previous laryngeal masks designed for example according to U.S. Pat. No. 4,995,388 (FIGS. 7 to 10); U.S. Pat. No. 5,241,956; and U.S. Pat. No. 5,355,879 provided channels to accept regurgitant fluids arising from the oesophagus in which the diameter of the channels is approximately constant and equivalent to the diameter of the constricted area of the anatomy known as the upper oesophageal sphincter. Such devices, once pressed against the sphinctral region provide conditions in which liquids arising from the oesophagus maintain approximately the same velocity as they pass through the tube of the device. Such devices, when correctly positioned, mimic the anatomy of the sphincter, but not that of the oesophagus, in which conditions of lower flow and therefore of higher pressure prevail during reflux of fluids. Such a position of the device may be undesirable however, because the principal object of such devices having a drainage tube communicating with the oesophageal opening is to avoid leakage of any gastric fluids arising from the oesophagus from leaking around the sides of the device, because such leakage risks contamination of the larynx by these fluids with consequent grave risk to the patient.
Furthermore, existing devices provided with gastric drainage tubes do not have tubes with a diameter as great as that of the oesophageal sphincter and therefore can only offer an increase in velocity of fluids entering the drainage tube, which as seen above results in a reduced pressure in the narrower tube, which will tend to cause fluids from the higher pressure region to force the distal end of the device away from the sphincter.